Influence on optical properties and switching durability by introducing Ta intermediate layer in Mg–Y switchable mirrors

Abstract

Magnesium–yttrium alloy switchable mirrors capped with a Pd layer with a thickness of 7.5nm have been shown to have a high switching durability of over 10,000 cycles between reflective and transparent states. However, the durability decreased considerably when the Pd thickness was decreased to improve the transmittance in the transparent state. Switchable mirrors with a thin Ta intermediate layer inserted between Mg–Y alloy layer and thinner Pd layers were then prepared by a direct-current magnetron sputtering method, and the optical switching durability was studied. Such a mirror capped by a Pd layer with a thickness of 3nm had a high switching durability of over 10,000 cycles, although a mirror without the Ta intermediate layer capped by a Pd layer with the same thickness never changed from the reflective to the transparent state. Owing to the decrease of the Pd thickness from 7.5 to 3nm, the visible transmittance in the transparent state increased, respectively, from 32% to 44% with high switching durability. The results of X-ray photoemission spectroscopy and transmission electron microscopy showed that the inserted Ta layer fully inhibits alloying between the Pd and Mg–Y layers, and that the Pd existed at the surface region and scarcely diffused into the Ta and Mg–Y layers even after switching of 10,000 cycles. Because alloying is one of the main reasons for the reduction in durability with decreasing Pd thickness, the prevention of alloying is expected to cause high switching durability.